The invention relates to a method for determining the saturation temperature of a solution in which the temperature of the solution in an optical measurement vessel is gradually increased from a temperature at which the solution contains crystals of the dissolved substance to a temperature at which all crystals are dissolved, the temperature meanwhile being measured continuously, a beam of light is transmitted through the measurement vessel and the dissolution of the last crystals present is detected optically.
Such a method is known from United Kingdom patent application No. 2,072,845. In said known method a beam of normal white light is used and the increase in intensity of the transmitted beam of light is detected at the moment the last (light-absorbing and scattering) crystals dissolve. The disappearance of the last crystals brings about only a slight increase of the light intensity, and therefore the moment at which this happens and the pertaining temperature cannot be determined fully accurately.